Method and apparatus for reducing damage associated with detonation and/or destructive knock

ABSTRACT

A piston for attentuation of detonation in the combustion chamber of an internal combustion engine has a top wall accommodating a cap. The cap has a flush extension of the cylindrical portion of the side wall of the piston and a transverse wall projected generally upward from the top wall of the piston. The transverse wall has a convex curve with a radius center located along the outer edge of the top wall of the piston in contiguous relationship to the ignition point of the air/fuel mixture in the combustion chamber. The transverse wall of the cap is located generally normal to the direction and movement of the flame front commencing from the ignition point and provides an abrupt increase in the cross sectional area of the combustion chamber in the direction of travel of the flame front to attenuate detonation in the combustion chamber.

FIELD OF INVENTION

The invention is in the field of reciprocating piston internalcombustion engines having piston and cylinder structures shaped toreduce damage associated with detonation and/or destructive knock.

BACKGROUND OF INVENTION

The thermal efficiency of an Otto cycle internal combustion enginedepends on the compression ratio. An increase in the compression ratioincreases the thermal efficiency of the engine and frequently entails anincrease in the tendency of the engine to knock. Compression ratios ofthe spark ignition engine are now limited by knock.

The knock in internal combustion engines is associated with the soundsthat are created by the engines. Knock associated phenomena cansometimes destroy an engine within minutes. Destructive knock may beassociated with detonation during the combustion of the fuel in thecombustion chamber.

Flames in the combustion chamber may propagate through the combustiblemixtures either as deflagrations or as detonations or they may originateat spontaneous ignition sites. Deflagrations are subsonic and associatedwith small spatial pressure variations. Detonations are supersonic. Theyare associated with large pressure discontinuities and impact pressures.The pressure discontinuities and impact pressures can cause the damageassociated with knock.

Conventional combustion chamber design is such as to promote turbulence.The cross sectional area of the combustion chamber decreases in theregion of the end gas to produce a quench or squish zone. Withoutturbulence, the highly agitated motion of the fuel air mixture, slowcombustion would result in inefficient operation of the engine. Thisshape of the combustion chamber does not inhibit detonation.

Detonation in an internal combustion engine chamber produces sound andpressure stresses. Various devices have been proposed to eliminatedetonation by attenuating the high amplitude of these pressure stresses.Bodine, in U.S. Pat. No. 2,760,472, utilizes a sound wave absorber padbetween the block and the head to attenuate the high amplitudedetonation into sound waves. The piston has a truncated inverted coneshape. Kydel et al. discloses, in U.S. Pat. No. 2,826,185, an internalcombustion engine having a piston equipped with a projection. Theprojection is mounted on top of the mid-section of the piston and hasdownwardly and outwardly sloping flat surfaces. The head is providedwith a firing chamber that decreases in size toward the center of thepiston. Polza, in U.S. Pat. No. 2,969,786, shows an internal combustionengine having a piston with an angularly related face providing a firingchamber adjacent to a spark plug. Burnham, in U.S. Pat. No. 4,046,116,shows a piston for an internal combustion engine carrying a plate toincrease the compression ratio of the engine. The plate has an upwardlysloping side wall facing the valves to provide clearance for the valves.Takeshi, in U.S. Pat. No. 4,162,661, shows a piston for an internalcombustion engine having two separate raised portions located at twoperipheral portions of the top of the piston. The ends of the raisedportions have concave surfaces to provide for mixing of an air/fuelmixture to enhance combustion and increase engine output power. Thery,in U.S. Pat. No. 4,235,203, shows a two-zone combustion chamber formedby a piston having an upwardly directed projecting part that divides thecombustion chamber into two portions. The projecting part has a channelproviding communication between the parts of the combustion chamber.These piston structures and combustion chamber shapes have some effecton detonation, but do not control detonation to allow high compressionratios without damage to the piston and head.

SUMMARY OF INVENTION

The invention is directed to a method and piston and cylinder structureof an internal combustion engine for preventing destructive detonationin the combustion chamber of the internal combustion engine. Thecombustion chamber of the invention formed by the piston face and headhas a configuration that attenuates detonation during the combustionepisode of an internal combustion engine.

In the method of reducing detonation in an internal combustion engine,the air/fuel mixture is introduced into the combustion chamber duringthe intake stroke of the piston means. The piston means compresses theair/fuel mixture. A spark ignites the compressed air/fuel mixturecausing combustion or burning of the air/fuel mixture. The burning rateof the air/fuel mixture is dependent on turbulent gas flow motions. Theturbulence affects flame speed and detonation. The flame front movesacross the combustion chamber. During this movement, there is an abruptincrease in the cross sectional area of the combustion chamber in thedirection of the flame travel causing an attenuation of the detonationwave and/or an incipient detonation wave, thereby inhibiting damagingknock. In one embodiment of the method, the flame front initially isdirected into diverging paths, including a central path, which isdivided into secondary diverging paths. At the terminal portions of allthe paths, there is an abrupt increase in the cross sectional area inthe direction of the flame travel, of the combustion chamber, causing anattenuation of the detonation wave or of an incipient detonation wave,thereby inhibiting damaging knock. The burning fuel mixture forms anexpanding gas that is utilized in the power stroke of the engine. Thecycle of the engine is completed by the exhausting of the gas in thecylinder prior to a subsequent intake of the next air/fuel mixture.

According to the invention, there is provided a cap means for a pistonof an internal combustion engine provided with an abrupt angled wallproviding an abrupt increase in the cross sectional area of thecombustion chamber in the direction of the flame travel across thecombustion chamber which attenuates detonation and/or incipientdetonation. In one embodiment, the wall extends transversely across thediameter of the top of the piston and has an angle of substantially 90degrees with respect to the top of the piston. In another embodiment,the wall has a convex curve with a radius of curvature centered at theelectrodes of the spark plug. The wall curves across the mid-section ofthe top of the piston and has an angle of substantially 90 degrees withrespect to the top of the piston. The angle of the wall with respect tothe top of the piston can have an angle of more than 90 degrees andstill achieve an abrupt increase in the cross sectional area of thecombustion chamber in the direction of movement of the flame front. Thecap means can be secured to the top of a piston or be integral with thetop of the piston. The cap means can have one or more divergent channelsproviding paths for dissipating detonation in an internal combustionengine. The channels terminate at the abrupt transverse wall providingan abrupt increase in the cross sectional area of the combustion chamberin the direction of the flame travel across the entire chamber, whichattenuates detonation and/or incipient detonation.

A specific embodiment of the internal combustion engine has cylindermeans with inside cylindrical walls surrounding piston means. Head meansmounted on the cylinder means form with the piston means a combustionchamber. Spark generating means, such as a spark plug, mounted on thehead means are operable to provide electrical energy to ignite acompressed air/fuel mixture in the combustion chamber. Cap means securedto or part of the top of the piston means has an abrupt step extendedacross the top of the piston generally normal to the direction ofmovement of the flame front, which results in attenuation of detonationand/or incipient detonation.

The cap means may have an upwardly and inwardly inclined front facedirectly opposite the ignition electrodes of a spark plug or means forgenerating an ignition spark. The front face may merge with a downwardlyor inwardly inclined rear face. The rear face joins a transverse wallextended across the piston top. The transverse wall extends in thedirection of movement of the piston generally normal to the top of thepiston. The front face has a central concave diverging channel andrearwardly converging arcuate walls which extend from opposite sides ofthe central channel to opposite ends of the transverse wall. The rearface has a pair of diverging channels located on opposite sides of thecenter portion of the cap means. The second channels extend to thetransverse wall. The flame front initially emanates from the region ofthe spark electrodes. The flame front moves upwardly through the pathformed by the central channel and outwardly and rearwardly through sidepaths adjacent side walls to the rear face. The flame front then movesover the transverse wall and is subjected to retardation due to theabrupt increase in the cross sectional area of the combustion chamber inthe direction of flame travel. This causes the attenuation of thedetonation and/or incipient detonation to permit the engine to operateat higher compression ratios, thus, without concomitant damageincreasing the thermal efficiency of the engine without damaging it.

IN THE DRAWINGS

FIG. 1 is a fragmentary sectional view through a cylinder of a prior artinternal combustion engine;

FIG. 2 is a diagram of normal flame speed behavior within a cylinder ofan internal combustion engine;

FIG. 3 is a top plan view of an Otto cycle internal combustion enginehaving the piston and combustion chamber of the invention;

FIG. 4 is an enlarged fragmentary sectional view taken along the line4--4 of FIG. 3;

FIG. 5 is a sectional view taken along the line 5--5 of FIG. 4;

FIG. 6 is a sectional view taken along the line 6--6 of FIG. 4;

FIG. 7 is a top plan view of the piston of FIG. 6;

FIG. 8 is a perspective view of the valve side of the piston and capsecured to the top of the piston of FIG. 4;

FIG. 9 is a perspective view similar to FIG. 8 of the spark plug side ofthe piston and cap thereon;

FIG. 10 is a vertical diagram of the combustion chamber with the pistonat top dead center;

FIG. 11 is a horizontal diagram of the combustion chamber with thepiston at top dead center;

FIG. 12 is a cylinder pressure-volume diagram comparing the engine ofthe invention with a prior art internal combustion engine;

FIG. 13 is a perspective view of a modification of the cap adapted to besecured to the top of a piston of an internal combustion engine;

FIG. 14 is a top plan view of a piston equipped with the cap of FIG. 13;and

FIG. 15 is a sectional view similar to FIG. 14 showing a piston equippedwith the cap of FIG. 13.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a fragmentary sectional view of apiston and cylinder structure of a conventional internal combustionengine. The engine has a block 10 having an upright cylindrical insidewall 11. A cylindrical piston 12 is located in sliding reciprocatingengagement with inside wall 11. Piston 12 is connected to a piston rod13, which has the usual bearing connection with a crankshaft (notshown). A head 14 is located over the block 10. Conventional head bolts(not shown) attach the head 14 to block 10. Head 14 has a generallycone-shaped combustion chamber 16 located in alignment with the top ofpiston 12. An intake valve 17 reciprocally mounted on head 14 isoperable in response to a rotating cam to selectively open and closeintake passage 18 for carrying an air/fuel mixture to combustion chamber16. An exhaust valve 19 mounted for reciprocal motion on head 14 isoperable to selectively open and close exhaust passage 21 for carryingexhaust gases from combustion chamber 16 to an exhaust manifold (notshown). A second rotating cam (not shown) is operable to reciprocateexhaust valve 19.

A spark plug 22 is mounted on head 14 between the valves 17 and 19.Spark plug 22 has spaced electrodes 23 and 24 located in the central topportion of combustion chamber 16. When an electric potential is suppliedto spark plug 22, an ignition spark between electrodes 23 and 24 ignitesthe air/fuel mixture in combustion chamber 16. The ignition of theair/fuel mixture in the combustion chamber 16 originates at spark plugelectrodes 23 and 24 and radiates therefrom in a flame front. The flamefront, illustrated as line 25 in FIG. 2, is divided into four combustionstages. In the final stage, the unburned compressed gas sometimesignites spontaneously before the arrival of the flame front. This isshown in FIG. 1 at 26, and may result in knock.

Referring to FIG. 2, there is shown a graphic representation indicatedat 27 of the burning velocity of the air/fuel mixture or flame front ina combustion chamber of an internal combustion engine plotted as afunction of the flame radius from the ignition location. The combustionepisode in chamber 16 is divided into four stages. The initial stage Iis the ignition of about 1% of the fuel mass. The second stage II andthird stage III is a rapid flame acceleration and exhibits the peakflame speed. In the final stage IV flame speed has a rapidde-acceleration as the flame front interacts with the head block andpiston walls. If detonation occurs instead, it moves at supersonicspeeds across the combustion chamber. It is accompanied by largepressure differences which can fatigue or damage engine components.Detonation in conventional internal combustion engines is now evited bymaintaining the compression ratio at relatively low values. This limitsthe thermal efficiency of the engine.

Referring to FIGS. 3 and 4, there is shown an internal combustion engineindicated generally at 28 having a block 29 and a head 37 attached tothe top of block 29 with a plurality of head bolts 43. Engine 28 is avalve-in-head engine having a plurality of reciprocating pistons 32operatively connected to a rotating crankshaft (not shown) withconnecting rods 35 in a conventional manner. As shown in FIG. 4, block29 has an upright inside cylindrical wall 31 accommodating areciprocating piston 32. Piston 32 has a generally flat circular topwall or face 33 and a cylindrical side wall 34 located in closeproximity to the inside cylindrical wall 31. Piston rod 35 is connectedto wall 34 with a wrist pin 36. A conventional bearing connects rod 35to the crankshaft whereby, on rotation of the crankshaft, piston 32reciprocates in the cylinder bore defined by wall 31. The engine has anOtto engine cycle wherein piston 32 has intake, compression, power, andexhaust movements.

As shown in FIG. 4, head 37 has a combustion chamber 42 located over topwall 33 of piston 32. Head 37 has a first generally upright and inwardlyinclined wall portion 44 having a threaded hole 46 accommodating a sparkplug 47. Spark plug 47 has electrodes 48 and 49 located in combustionchamber 42. Electrodes 48 and 49 are located generally along a diametricupright plane bisecting the top 33 of piston 32. Electrodes 48 and 49are positioned above an outer edge portion of piston 32.

Head 37 has a second wall portion 51 joined to the upper end of thefirst wall portion 44. Second wall portion 51 extends downwardly towardthe diametrically opposite side of piston 32 to converge the combustionchamber 42 to an area opposite spark plug 47. Wall portion 51 has portsaccommodating intake and exhaust valves. FIG. 4 shows the intake valve52 reciprocally mounted on head 37 for movement between the closedposition shown in full lines and an open position shown in broken lines.Conventional rotating cam and rocker arm structures are used toreciprocate valve 52. Valve 52 has a cylindrical head 53 joined to astem 54. Head 53 engages an annular valve seat 55 to close the intakepassage 56 leading from intake manifold 38 to combustion chamber 42.When valve 52 has been moved to the open position, as shown in brokenlines, the fuel/air mixture flows through passage 56 into combustionchamber 42. Head 37 is provided with an exhaust valve similar to valve52. The exhaust valve is operable to move between open and closedpositions to provide for the flow of exhaust gases from combustionchamber 42.

Referring to FIGS. 4-9, a cap or member indicated generally at 57 issecured to the top of piston 32 with a plurality of bolts 58. The bolts58 extend upwardly through the top wall 33 of piston 32 and are threadedinto suitable holes in cap 57. Other means, such as adhesives, can beused to secure cap 57 to top wall 33 of piston 32. Cap 57 can beintegral with the top of piston 32 so that the piston and the cap are aone-piece unit.

As shown in FIGS. 7, 8, and 9, the top wall or top 33 of piston 32 hasan annular rim 59 surrounding the outer peripheral edge of top wall 33.Cap 57 has a generally flat bottom 61 that is in surface engagement withtop wall 33. The outer edge of bottom 61 has an arcuate peripheralshoulder 62 that rests on a portion of rim 59. The top of piston 32 maybe flat. The cap for a flat top piston has a flat bottom secured to thepiston. Cap 57 can be integral with the top of the piston.

Cap 57 has an upwardly and inwardly directed forward or front, indicatedgenerally at 63, that is joined to a downwardly and inwardly slopingback, indicated generally at 64. Back 64 is joined to an end or wall 66that forms a step with top wall 33. Wall 66 located generally normal totop wall 33 of piston 32 extends across the diameter of the top ofpiston 32 generally normal to the direction of movement of the flamefront. Wall 66 provides an abrupt increase in the cross sectional areaof the combustion chamber portion 42B in the direction of flame travel.Wall 66 has a height of about 5 to 10 mm throughout its diametric lengthof about 8.5 cm. Other sizes and size relationships may be used toprovide wall 66.

As shown in FIGS. 5, 7, 8, 9, and 11, front 63 of cap 57 has a centralconcave first channel or pocket 67 extended from the lower edge of cap57 upwardly and inwardly toward the inner edge of the cap. Channel 67has opposite outwardly curved sides that diverge from the lower edge ofthe cap. The upper ends of the sides are joined to an inwardly curvedupper edge. The curved sides and curved upper edge have substantiallythe same curve lengths. The mid-portion of the curved upper edge islocated at approximately the mid-point of cap 57. The face of the bottomof channel 67 has a generally symmetrical radial concave curvature. Theradial concave curvature is larger than the lateral concave curvature.The center of channel 67 is located along and in alignment with thelongitudinal axis of spark plug 47. As shown in FIG. 4, front 63 isspaced from electrodes 48 and 49 of spark plug 47 providing combustionchamber 42 with an upwardly and inwardly inclined forward portion 42A.Chamber portion 42A diverges upwardly and inwardly from the outerperipheral edge of the top of cylinder wall 31 when the piston is in thetop dead center, as shown in FIG. 4. Back 64 slopes inwardly anddownwardly toward transverse wall 66 providing the combustion chamberwith a diverging or increasing cross sectional area 42B.

Returning to FIGS. 8 and 9, the front has convex side portions 68 and 69extended from opposite sides of pocket 67 to the transverse wall 66.Side portions 68 and 69 converge from the side edges of channel 67 tothe opposite ends of transverse wall 66.

Back 64 has a pair of shallow concave diverging channels or pockets 71and 72 separated by a downwardly and inwardly inclined mid-section orrib 73. Channels 71 and 72 are located on opposite sides of adiametrical plane bisecting channel 67 and provide second paths for theflame front and detonation energy. Channels 71 and 72 have identicalshapes and curvatures and extend from the top edge of channel 67 to thetransverse wall 66. The outside edge of channel 71 joins the uppercurved edge of side 68. The outside edge of channel 72 joins the upperedge of side 69.

Referring to FIGS. 10 and 11, there is shown a diagram of the combustionchamber 42 with the piston 32 in the top dead center at the completionof the compression stroke. The air/fuel mixture in combustion chamber 42has been ignited by an electrical spark generated between the electrodes48 and 49 of spark plug 47. The initial ignition occurs at theelectrodes 48 and 49 and commences a flame front that propagates in anarc from the ignition point in the radial direction from electrodes 48and 49 across combustion chamber 42.

The flame front moves from first path 79 and side paths 81 and 82 tosecond paths 83 and 84 provided by channels 71 and 72. Second paths 79and 81 diverge toward the middle transverse plane of the piston face 33and terminate at transverse wall 66. The flame front continues along thesecond portion 42B of the combustion chamber 42 into terminal portion 75of the combustion chamber. The flame front passes over transverse wall66. The abrupt or sudden change in the cross sectional area along thepath of the flame's travel of chamber 42B after wall 66 causesattenuation of detonation and/or incipient detonation. Channels 67, 71,and 72 and wall 66 increase the turbulence intensity of the air/fuelmixture and, thus, enhance combustion. The turbulent gas motionsthroughout combustion chamber 42 affect the burning rate of the fuel, aswell as the efficiency of the engine. This occurs simultaneously withthe attenuation of detonation or incipient detonation. The reduction ofdetonation or incipient detonation allows the engine to operate athigher compression ratios without incurring damage. The high compressionratios increase the thermal efficiency of the engine.

Referring to FIG. 12, there is shown a pressure-volume diagram for aconventional piston and cylinder of an internal combustion engine andthe piston and cylinder equipped with the cap 57 of the invention. Thedotted line curve 77 represents the pressure-volume curve in the fourstroke cycle of a conventional piston and cylinder arrangement. The fullline shows the curve for a piston equipped with the cap 57. There is asubstantial increase in the pressure of the air/fuel mixture in thecombustion chamber in curve 78 caused by the cap 57. This increase inpressure results in the greater efficiency and output power of theinternal combustion engine.

A modification of the cap for a piston of an internal combustion engineof the invention providing an abrupt increase in the cross sectionalarea of the combustion chamber in the direction of the flame fronttravel is shown in FIGS. 13-15. Referring to FIG. 13, cap 100 is aone-piece metal member having a generally semi-circular outer edge 101curved to conform the outside of the top of a piston. Edge 101 has anarc of about 180 degrees. The edge can have an arc that is greater thanor less than 180 degrees. Opposite ends of edge 101 are located adjacentdiametrically opposite sides of the top of piston 107. Cap 100 has aconvex curved front wall 102. A radius center 103 midway between theends of outer edge 102 determines the radius of the arced front wall102. Radius center 103 is located in close proximity to the electrodesof the spark plug of the engine. Cap 100 has a generally flat top 104and a flat bottom 106. The cap 100 has a generally uniform thickness.Preferably, the cap 100 has a thickness of 7 mm. Other thicknesses ofthe cap can be used.

As shown in FIGS. 14 and 15, cap 100 is located on the top 108 of piston107. The cap has a plurality of holes 109 accommodating bolts 111secured to the top of piston 107. Other attaching structures can be usedto secure cap 100 to the top 108 of piston 107. Cap 100 can be integralwith the metal of piston 107.

Referring to FIG. 15, there is shown an internal combustion engineindicated generally at 112 similar to the engine 28, shown in FIG. 3,having a block 113 and a head 117. Block 113 has a generally uprightcylinder 114 reciprocally accommodating piston 107. Piston 107 isattached to a connecting rod 116 operatively connected to a rotatingcrankshaft (not shown). The upper end of cylinder 114 and head 117 formsa combustion chamber 118 located over the top of piston 107. The head117 has a threaded hole 119 accommodating a spark plug 121. Spark plug121 has electrodes 122 and 123 located above an outer edge portion ofpiston 107. The head 117 has a passage or port 126 terminating in anannular valve seat 124 open to combustion chamber 118. A reciprocatingvalve indicated generally at 127 cooperates with the head and seat 124to control the flow of air/fuel mixture into combustion chamber 118. Aconventional rotating cam and rocker arm structure (not shown) is usedto reciprocate valve 127. Valve 127 has a cylindrical stem 128 integralwith an annular head 129. The head 117 is provided with an exhaust valvesimilar to intake valve 127.

Cap 100, as shown in FIGS. 14 and 15, is secured to the top 108 ofpiston 107 with the bolts 111. The radius center 103 is located in closeproximity to the spark plug electrodes 122 and 123. The outer edge 101is located in vertical alignment with the outer wall of piston 107. Thislocates the front wall 102 of cap 100 across the mid-section of pistontop 108. The central portion of wall 102 is located slightly forward ofthe center of top 108. Front wall 102 projects upward generally normalto the top of piston 107 and extends to opposite portions of the pistontop.

As shown in FIG. 15, piston 107 is in the top dead position at thecompletion of the compression stroke. The air/fuel mixture in combustionchamber 118 is compressed and has been ignited by the electrical sparkgenerated between electrodes 122 and 123 of spark plug 121. The initialignition of the air/fuel mixture occurs at the electrodes 122 and 123and commences a flame front that propagates in a generally radialdirection, indicated by arrows 131 in FIG. 4, along an arc from theignition point across the combustion chamber 118. The flame front passesover the generally transverse wall 102, thereby suddenly encountering anincrease in cross sectional area of the combustion chamber in thedirection of the movement of the flame front. The abrupt change in thecross sectional area along the path of the flame front travel of thecombustion chamber causes attenuation of detonation and/or incipientdetonation. The abrupt change in the cross sectional area of thecombustion chamber is generally normal to the direction of movement ofthe flame front. The reduction of the detonation and incipientdetonation allows the engine to operate at a higher compression ratiowithout incurring damage. The higher compression ratios increase thethermal efficiency of the engine.

While there has been shown and described the several preferredembodiments of the piston, cap, and combustion chamber of the invention,it is understood that changes in the size, shape, and structure may bemade by those skilled in the art without departing from the invention.The invention is defined in the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A piston for attenuation of detonation in an internal combustion engine having a combustion chamber accommodating and air/fuel mixture, said mixture when ignited forming a flame front that propagates across the combustion chamber comprising: a cylindrical side wall, a top wall having a center being secured to the side wall, and cap means joined to the top wall, said cap means having a generally semi-circular outer edge curved to conform to the size and shape of the cylindrical side wall, said outer edge being a flush extension of a semi-circular portion of the cylindrical side wall, said cap means having a transverse wall projected generally upwardly from said top wall extended between opposite ends of the semi-circular outer edge, said transverse wall having a convex curve with a radius greater than that of a radius of said top wall being entirely on one side of a plane passing through said center opposite that of a radius center located on said outer edge midway between the ends thereof, in contiguous relation to the ignition point of air/fuel mixture in the combustion chamber, said transverse wall being located generally normal to the direction of movement of the flame front commencing from the ignition point in the combustion chamber.
 2. The piston of claim 1 wherein: said piston has a flat top surface, said transverse wall extended upwardly normal to said flat top surface of the piston.
 3. The piston of claim 1 wherein: said transverse wall projects upwardly generally normal to the top wall of said piston.
 4. The piston of claim 1 wherein: said transverse wall has opposite ends located adjacent opposite diametric portions of the top wall of the piston.
 5. The piston of claim 1 wherein: said cap means has a generally flat top surface.
 6. The cap of claim 1 wherein: said member has a generally flat top surface.
 7. A cap adapted to be mounted on a top wall of a piston of an internal combustion engine for attenuation of detonation in a combustion chamber of the internal combustion engine, said piston having a cylindrical side wall comprising: a one-piece member adapted to be secured to the top wall of the piston wherein said top wall has a center, said member being smaller than the top wall of said piston and having a generally semi-circular outer edge curved to conform to the size and shape of the cylindrical side wall, said outer edge being a flush extension of a semi-circular portion of the cylindrical side wall, said cap having a generally upright transverse wall extended between opposite ends of the semi-circular outer edge, said transverse wall having a convex curve with a radius greater than that of a radius of said top wall being entirely on one side of a plane passing through said center opposite that of a radius center located on said outer edge midway between the ends thereof, in contiguous relation to the ignition point of air/fuel mixture in the combustion chamber, said transverse wall being located generally normal to the direction of movement of a flame front commencing from the ignition point in the combustion chamber of the engine.
 8. The cap of claim 7 wherein: said cap has a flat top surface and a flat bottom surface, said transverse wall extended normally between said top and bottom surfaces.
 9. The cap of claim 7 wherein: said transverse wall projects upwardly generally normal to the top wall of said piston.
 10. The cap of claim 7 wherein: said transverse wall has opposite ends adapted to be located adjacent opposite diametric portions of the top wall of the piston means.
 11. An internal combustion engine including block means having a plurality of cylindrical walls accommodating reciprocating piston means, head means mounted on the block means, said head means and piston means enclosing combustion chamber means, each of said piston means having a top wall having a center and a cylindrical side wall, said combustion chamber means accommodating an air/fuel mixture, said mixture when ignited forming a flame front that propagates across the combustion chamber means, the improvement of: cap means joined to said top wall of the piston means, said cap means having a first wall section spaced from said top wall of the piston means, a generally semi-circular outer edge curved to conform to the size and shape of the cylindrical side wall of the piston means, said outer being a flush extension of a semi-circular portion of the cylindrical side wall, and a transverse wall projected upwardly from said top wall of the piston means between opposite ends of the semi-circular outer edge, said transverse wall have a convex curve with a radius greater than that of a radius of said top wall being entirely on one side of a plane passing through said center opposite that of a radius center located on said outer edge midway between the ends thereof, in contiguous relation to the ignition point of air/fuel mixture in the combustion chamber, said transverse wall being located generally normal to the direction of movement of the flame front commencing from the ignition point in the combustion chamber thereby providing an abrupt increase in the cross sectional area of the combustion chamber means in the direction of travel of the flame front whereby detonation in said combustion chamber means is attenuated.
 12. The engine of claim 11 wherein: said piston has a flat top surface said transverse wall extended upwardly normal to said flat top surface of the piston.
 13. The engine of claim 11 wherein: said transverse wall projects upwardly generally normal to the top wall of said piston means.
 14. The engine of claim 11 wherein: said transverse wall has opposite ends located adjacent opposite diametric portions of the top wall of the piston means.
 15. The engine of claim 11 wherein: said first wall section has a generally flat top surface. 